This invention relates to means for generating the pitch signal for use with aircraft head up displays and more particularly to compensating the computed pitch signal for long term errors in a gyroscope and unexpected shifts in the air mass.
Prior art pitch computation circuits are disclosed in Astengo, U.S. Pat. No. 3,744,309, and Muller, U.S. Pat. No. 3,851,303, both of which are assigned to the assignee of this application. It is important to have the computed pitch signal as accurate as possible since an accurate pitch signal is required for use with the aircraft head up display devices such as those disclosed in Bateman U.S. Pat. No. 3,654,806; Bateman U.S. Pat. No. 3,686,626 and Kirschner U.S. Pat. No. 3,816,005 all of which are assigned to assignee of this application. As may be appreciated from the examination of the foregoing patents, an accurate pitch signal is highly desirable for the proper operation of these head up display instruments especially when they are used during aircraft landing operations.
In the computed pitch circuit as disclosed in the Muller U.S. Pat. No. 3,851,303 a longitudinal accelerometer signal is compensated by means of a signal representing the differentiated air speed of the aircraft so that the longitudinal accelerometer provides a reasonable accurate indication of the aircraft's pitch attitude. However, when the air mass itself is changing velocity, the air speed input to the system can introduce an error into the pitch computations.